Butler Hospital’s striking workers and management are scheduled to resume talks with a federal mediator on Wednesday, marking the first formal negotiations since the union last week rejected the hospital’s “revised last, best, and final’’ offer. However, Butler Hospital leaders and members of its negotiating team “have had several meetings with SEIU officials since the start of July,’’ Mike Raia, a hospital spokesman, said in an email. Federal law prohibits striking workers from being permanently replaced if the strike is to protest an unfair labor practice committed by their employer. As of Tuesday, Butler Hospital had 375 job openings, according to its careers website. Butler Hospital is about 70% publicly funded, Marran, the hospital’s president, said, through reimbursements from federal Medicare and Medicaid insurance, which typically pay far lower rates than private insurers.